Tractor steering mechanism



Oct. 21, 1952 c, us Fso 2,614,644

TRACTOR STEERING MECHANISM Filed Jan. 3. 1949 8 Sheets-Sheet l IN VEN TOR.

ATTORNEY C.A.GUSTAFSON TRACTOR STEERING MECHANISM Oct. 21, 1952 Filed Jan. 3, 1949 8 Sheets-Sheet 2' ad am JAIYYUUMETT Oct. 21, 1952 c. A. GUSTAFSON TRACTOR STEERING MECHANISM 8 Sheets-Sheet 3 Filed Jan. 5, 1949 IN V EN TOR.

m RV Q N. NV ww Q a NM l m ATTORNEY Oct. 21, 1952 c. A. GUSTAFSON 2,614,644

TRACTOR STEERING MECHANISM I ATTORNEY Oct. 21, 1952 c. A. GUSTAFSON 2,614,644

TRACTOR STEERING MECHANISM I s Sheets-Sheet 5 Filed Jan; 5, 1949 INVENTOR;

far/4. 6611/6/10 ATTORNEY I Oct. 21, 1952 c. A. GU$TAFSON TRACTOR STEERING MECHANISM 8 Sheets-Sheet 7 Filed Jan. 3, 1949 IN VEN TOR.

c. A. GUSTAFSON TRACTOR STEERING MECHANISM Oct. 21, 1952 8 Sheets-Sheet 8 Filed Jan. 3-. 1949 R: m NW. 62 A Q M ATTORNEY Patented Oct. 21, 1952 ".UNITED STATES. PATENT other I I macros v i Q I, I

Carl A. Gustafsom Peoria, 111., assigiior to Cater-- pillar Tractor '06., Peoria, .Ill.-, a corporation of Galifornia Appiioa'tionJanuai-y 3, 1949, Serial'No. 683.77

'Ihis invention relates to steering 'mecharfisms and particularly to a mechanism for"; effecting articulation or steering between a pivotali con- In the past, several difiererit types of hydraulic steering controls have been providedfor two.

:wheel tractors comprising hydraulic jacks which are supplied with fluid pressure controlled by the tractor steering wheel. 7 However, the control is generally arranged to sheet-steering upon turning of the wheel and to continue to direct fluid to the jacks 'tofiefiect turning of the tractor relati've to. the drawn vehicle until such time 'as the steering-wheel is again returned to its normal position. i This is not desirable as it does not give the operatorthe usual feel of stecringarid unduly v complicates his work. Furthermore, conventional hydraulic steering controls for two-wheel tractors are in most'cases hrovided with a single "pair 'of' 'hydraul'ic jacks-or even a single jack which must he very large to provide torque for steeringandare incapable of effecting a sharp turn-wherein the tractor assumes aposition. at right angles to the drawn vehicle.

It is, therefore, an. object or this inventionv to .provide e.- steering. eontrol iorza two-wheel tractor :comprising'two pairs of hydraulic jacks for effecthig steering, the jacks being arranged to double the: turning torque obtainable with a single pair .of hydraulic jacks. i Another object of two pairs of'hydraulic jacks for steering avtwothis invention is to provide by a steering wheel in which the rate of fliiid new to the jacks changes in response; to the speed at which the steering wheel is turned; r

Other objects and advantages fthis i-iiventioh are made apparent inthe' renewing specification byref'erence to the'accom ea-laying drawings; v In the drawings:

Fig. 1 is a planview of a two-wheel'- tractorand scraper combination, the tractor eing shown turned 9'0fre1ative totheseraper; Fig. 2 'is an enlarged fragmentary side elevational View ofthe steering arrangement Efidhifitth between the tractor and the scraper; portions of theview being broken away and shown to more clearly illustratejthe inecli-a'r'1ism 3 is a schematic horizontal sectional of the hydraulic jacks which serveto efieet ing ofthetractor;. r Fig. 4' is an enlarged; sectional vi-ewtaken through oneof the hydrauhcjacks; f

Fig. '5 is adiagrammatic illustration of the composite steering mechanism for" the two-whee tractor comprising the steefihg Twheel and the hydraulic; j'acks; 1 v

Fig. 6' is an: enlarged: sectional View or. the tractor steering wheel; Fig. '7 is a fragmen-tary section 1: view ltalz'eni'n a plane indicated by the line VII-" 4711 in Fig. 6; Fig. 8 is a schematic disclosure of thefl-uidsuhply' circuit; and

section Fig. 9- is a schematic d-iselosureoi a modined form of the control :valve and hydraulic circuit.

' The steering arrangement for'the combination pivoted at one end on apart or the tractor,; while their opposite ends are" pivotally connected. to

wheel tractor, the jachsbeing arranged to work I simultaneously in eff-(acting a 90 turn of: the trac 'tor relative to a drawn vehicle.

Another object of this invention is to provide a steering mechanism with twopairs of hydraulic Jack's for effecting steering of. a two-wheel tractor in which the pistons andthe connecting rods of the jackshave suitable fluid passages to reduce *thenecessity of exterior pipe and connections.

" Another object of this invention isto provide j steer'ng mechanism with jacks supplied'with fluid pressure by a fluid supply circuit controlled by a steerhg wheel in a manner tosupply fluid to the jacks only when thesteering wheel is being turned. g I

' Another object of' invention is to provide steering mechanism havin jacks suppliedwith fluid pressure by afluid simplycircuit controlled arms of a lever v6 that free torotate about the axis of a kingpin t.- The other pairiof jacks-8 and 9 are each pivoted. at one end to thescraper while their opposite endsare likewise iiivo'td to m nfi VerB in a manner to b-Siibseqiienty described;

. sshown in Fig. 2; a bracket l li i'sfhin'ged as at I! and I37 to'the tractor .franie'jlhthei' ass r. the hinge connections 1 21 and. 13' Being argued. Bracket is provided with spaces tearin -s l6 and I1, while the draft connection f8 of'the scraper is provide .withspace'd bearin s it; and 2| and received between the bearings 19'" d 2| is the hub or a four armedlever 'flwhich'is re to turn" about the a-Xisof kingpin 1'. Lever 6,

as best shown in Figs. and f, 'isproifiidedwith spaced arms to e acuofwhich one -=nd of one or the jacks-1, 4; a and e ispivot n ccnnected.

Fig. 3.

v.and 44. '46 located within the piston rod and serves to connect passage 43 with the cylinder beyond the to the bracket II as by pins 23- and 2! respec- I tively; whereas, the jacks 8 and 9 are each pivoted to the scraper draft frame 18 as by pins 28 and 23 respectively, this arrangement being clearly shown in Fig. 3 of the'drawings. Pistons 3| and rods 32 are associated with the jacks 3 and 4 and the rods 32 are pivotally connected to lower. arms of lever B, one of which'is shown at 34 in Fig. 2. Corresponding pistons 33 and rods 31 are associated with the hydraulic jacks 8 and 9 and the rods 3'! are pivotally connected to upper arms 38 and 39 of lever 6.

It is desirable that all four of the hydraulic jacks have the same length stroke in order to accomplish proper steering of the tractor. Since the spacing of the pivotal connections 26 and 21 for jacks 3 and 4 is less than the spacing of the pivotal connections 23 and 29 for the jacks 8 and 3,;the arms of the lever 6 are disposed at a slight angle toward the pivots 25 and 2'! to equalize the distances between the opposite ends of each of the several jacks when the steering mechanism is in a central position as shown in Fig. 3.

To eifect turning of the tractor relative to the scraper, the jacks in each pair operate oppositely to each other. For example, when the jacks 3 andB are retracted. the jacks 4 and 3 are extended, swinging the tractor to the right relative to the. scraper as illustrated in Fig. 1.

Conversely, when fluid is directed to the jacks to effect steering to the left, then the jacks 4 and 9 are retracted and the jacks 3 and 8 are extended. The jacks 3 andB alone or the jacks 4 and 9 alone are capable of effecting the steering Just described. Jacksareemployed in pairs, as

shown, to obtain a high turning torque with jacks of minimum size and capacity.

The conduit system associated with the jacks is designed to eliminate unnecessary external piping and is diagrammatically illustrated in Power lines 4| and 42, leading from a source of fluid under pressure, are associated with the jacks 3 and 4 to direct fluid simultaneouslyto all of the jacks by way of fluid directing'passages in. the piston rods 32 and 31. Pressure in line 4| retracts the pistons 3i and 36 in jacks-3 and 8 and extends the pistons 3! and 36 in the jacks 4 and 9. directed through the power line 42 will extend the pistons 3| and 36 of the jacks 3 and B and Fluid pressure retract the pistons 3| and 36 of the jacks 4 and 9. x The hydraulic jack shown in Fig. 4 of the drawings represents the jack shown at 4 in Fig. 3

but is typical of any of the jacks 3, 4, 8 and 9. Its piston rod 32 adjacent its pivotal connection with lever arms 6 is provided with passages 43 Passage 43 communicates with a pipe municates with the cylinder on the opposite side of the piston by way of ports 48 located in the piston rod adjacent the, piston. Thexrod end of .draft frame l3.

'of jacks 3pand 4 :communicate with corresponding passages in the pistonrods 31 of jacks 8 and 9 by way of junction blocks 52 and 53 (Fig. 2), the junction blocks being coupled together by suitable flexible hose couplings 54 and 55, only one of which is shown in Fig. 2 of the drawings and both of Whichare shown schematically in Fig.3. Thus, when fluid is directed through the power line 4| to retract the pistons associated with the jacks 3 and 8 and at the same time extending the pistons associated with the jacks 4 and 9, the fluid from power line 4| will first enter the head end of jack 4 and the rod end of jack 3. From the rod end of jack 3, fluid will enter passage 4'! in rod 32. and then will flow to a corresponding passage 41 in rod 31 by way of cored passage 44, junction blocks 52 and 53, and flexible hose coupling 54. Consequently, fluid from power line 4'! will be directed to the rod ends of both the hydra'ulic jacks 3 and 8. At the same timefluid from power line'4l is directed to the head end of jack.4 where it will flow through passage 43 of piston rod 32 and then a corresponding passage 46 in piston rod 31 of jack 9 by way of cored passages 43, junction blocks 52 and 53, and the flexible hose 55. As a result, fluid pressure is exerted at the head ends of boththe jacks 4 and 9 and at the rod ends of both the jacks 3 and 3. When fluid is directed through oppositely arranged power line 42, it flows simultaneously to all four jacks to extend the piston rods of jacks 3 andld and to retract the piston rods of jacks 4and 9. Whenfluid is directed through either power line, the displaced fluid from the jacks is returned to the source of supply by wayo'fthe other line.

In order to provide a stable connection between the tractor and scraper when the vehicle is traveling .in a straight forward direction, it is desirable that the arms of the lever 6. be substantially normal to the longitudinal axis of the vehicle, as isshown in Fig. 3 of the drawings. Due to the fact that frictional" drag of the, fluid flowing through the passages in the piston rods to the diflerent hydraulic jacks could is traveling in a straight forward direction. To

prevent such non-uniform action and to insure synchronous operation of all of the jacks, the lever 6 is geared to the bracket H to cause it to pivot about the axis of king pin l at onehalf the angular speed that the bracket l I pivots about theaxis of theking pin. This gear ratio insures a position of the lever 5 when the tractor and scraper are aligned. The gearing is shown in Figs. 2 and 3 as a quadrant gear 6i carried on bracket H and meshing with a pinion 32 fixed to a shaft 63. Shaft 63 is journaled in spaced bearings supported in the scraper Directly below and also fixed to shaft 63 is a pinion 64 (Fig. 2) which meshes vWith a se m scares rigidly secured to lever B.-

. 1+ non-"rotatably' secured to a I having a telescopic spline'doonnection 82 with a eeaxially 'aligned shaft yldedzwith a threaded portion '84interposed be- I a shaft '89.

asegment gear 94.

I housing 91'.

1 linkage which connects lever 9'! 1- adre a ne w ea e Spool amass;

I h two to one fists between t e angular "movement of bracket II and lever tfi-Consequeritly,-as the hydraulic jacksareactitrated-the tractor and its bracket II will turn v about-the king pin 1 *at twice the speed and through double the angular distance of the lever 6-. "Therefore with this arrangement and when the tractor is traveling in; a straight forward directionfthe arms of lever 45 will always be substantially normal to the longitudinalaxis ofv the vehicleg-thus, always providing a stable connec tiorrbetween the tractornandthe scraper. Moreover, with this positive gear drive between bracket I-I- and lever 6,- the pistons in the :respective-'-' hydraulic jacks rnust all -'move synchronously and at the same rate-regardless of anypres'sure-drop-in thefl'uid to any particular -ThE general steering arrangement is-;il-lustreated schematically in Fig. 5 and comprises a eoritrel-" valve 12 and a-valve spool 16 3 adapted -f'or *-reci procal movement therein to. direct fluid under pressure to powerlines 4-! and 42 thereby actuating the jacks in scribed} Valve spool 16 is actuated-through link amanner previously dememb'ers IT-and 18 from amanuallycontrolled steeringmechanism"enclosed-within a housing I H As *isbest illustrated in 'Fig. 6,- the manual steeringmechanism -comprises a steering wheel steering post SI 83. Shaft 83 ispro tween a pair of spaced collars 36 and 81. Collar "fl'is provided with'a groove which is received anend of a lever -88 that is rigidly secured to shaft- 89 extends through a wall of the-housing member SI and has rigidly secured to its-outer end the lever lBshown in Fig. 5. A nut 92 having threaded engagement with the threaded portion of shaft 83 is provided with a straight rack--=gear ea -which meshes with Segment gear 94 is fixed to ashaf-t 96, jourrialed inand'extending through of theshaft flfi-which-extends through housing Blisa lever 91, the lever-91 being pivotally con- *riected to-one' end of a rod-98; th'eopposite end ct -which is 'pivotally connected to one arm of lever GrjLin'k Sh-and lever 91 may be referred "to as" 'follow-up linkageserving automatically to .eturnithespoolvalve '16 to aneutral position whenever the "steering wheel is not in motion.

"operation, turning-"of steering wheel I l efdirection a shoulder of housing 9I. Nut 92 is held a'gainst vertical "movement with shaft 83 'during' initial turning, of "the steering wheel II by its engagementwith segment 94, the segment Rigidl'y secu'redto the outer; end

I ct axial movementof'f'shaft.83, such move- 1 men being, limitedby engagement of collar 86 'with'Ia'Ishoulder ofihousinglil in one.

"and in the opposite direction by engagement of V sonar '81 with 6 the right todirect line- H. This effects steering to theright and incidently also. causes swinging movement of lever v 6 about the axis of king pin I.

will effect'the follow-unlinkage connecting-lever f 6 with lever 91 (Fig. and will result in thesegment=94 rocking withthe shaft 96 andib-y its engagementwith rack -93 of nut 02'; the shaft 83 will beflr'eturned to a neutral position without turning of steering wheel 1 I. Returning of shaft 83 to its neutral position shown in Fig. -'6 will, through levers *88 and -'I8,"position spool valve .16 of control vvalve T2 to a neutral position and thereby shut off the flow of fluid to either of the power lines M and 42 which are connected to the pairs of hydraulic jacks. Thus as the steering wheell-I is rotated, the control valve will operate to direct fluid to the J'acksfor -=effecting steering of the tractor relative to the scraper.

However, when the steering wheel isheld stationary in any position, the control valve- 12 will automatically be returned to its neutralpos'ition.

' With the arrangement shown in Fig.6, in the event offailure of the fluid pressure to the hydraulic jacks, the tractor "will be looked in steered should occur.

position, at'least for a sufficient time forthe opverator ,to apply the brakes to stop thevehicle train. This is so since there is a direct connection of the linkage between "lever 9'! and lever B. Upon'such failure, tendencyof the'tractor to swing relative to the traileris' resisted through this'linkage between lever 51 and lever B. This linkage becomes substantially locked by' virtue of connection thereof to the sets of gearing 93, 0'4,"a nd"6I, 62, 64 and BB, and will remain locked unless the forces to -which it may be subjected upon power failure as the vehicle trainmoves are great enough to break the same. However, therewill be sufficient time for the operator to apply the brakes before such breakage The collars 8B and 81 also serve to prevent damage to the spool valve T6, particularly in the case of oil failure o'f'the fluid supply circuit as they prevent any tendency of the steering mechanism to pull :the spool entirely out of its. housing. The fluid supply circuit :for this steering control is, diagrammaticallyshown inFig. smof the drawings in whieh'the control valve .12 "and a pilot valve '13 are shown in section. Spool 1B, which "is axially .slidable .in the control valve 12, serves to open and close passagesfor directingfluid to either of the power lines ll and 4.2. 'Control Valve" is provided with asupply passageIIlfi connected to :a pipe I01. Pipe I01 can beisupplied'with fluid-from either a large rotary sliding vanetype pumpI08 ora smaller rotary sliding vane type pump I09.

Both pumps I08 and I09 :receive fluid from a supply tank .15 byway of inlet line I10 and are driven from a suitable power take-off from the being 'held against movement by the followeup with lever 6. immature: can move axially with shaft 83 only when lever 6 rocks about the axis of king Q pin in response to actuation of the steering jacks; 1'1herefore, initial turning ofthe steering wheel. .II' turns the shaft 83 and advances it axially in one direction or the other.

Ass": ng the steering wheel 'I-l to be turned blockwise'to raise the shaft fli then collar 31 'whiohhontrols: lever 88 will rise and through valve It to tractor. When the steering wheel II is rotated slowly, only the discharge from .the small pump I09 is directed tothe-pipe I0! and during this time the full discharge of the large pump I08 is returned to the supply tank 15. However, as the speedor rotation of thetractor steering wheel II is increased, the discharge from both pumps will be directed. to pipe I01 to increase the turning speed of the tractor relative to the scraper. This is accomplished by the pilot valve "I3 which has a spring loaded plunger I I2-, the .end'of the plunger carrying a :rollerwhich rides fluid under-pressureto power This movement spring loaded plunger II2 is a similarreaction plunger H3 which serves to prevent binding of the spool valve I6 as it is axially reciprocated within the control valve I2. V A pipe II4 connects pipe IIl'I with a chamber H6 in pilot valve 13, while a pipe II'I connects a low pressure chamberl I8 in pilot valve :3 with a return line I II,which return line connects the control valve I2 with supply tank I5. A. chamber I2I in pilot valve I3 is connected with a chamber I 22 in a housing enclosing a'shuttle valve I23 by means of a pipe I24.

In operation, if the steering wheel is being turned slowly, the spool valve I6 will be moved to the right or left, as viewed in Fig. 8, in order to direct fluid pressure from pipe II)? to either of the power lines 4| or 42 depending uponthe direction of turning of the wheel. As long as the steering wheel is rotated slowly, the spring loaded plunger I I2 of pilot valve 73 will be thrust against the ramp I26 of spool valve I6. During this time the discharge from small pump I63 will be directed through pipe It? to the control valve I2 and then to either one of the Dower lines 4i 2 or 42 depending upon which direction the spool valve I6 has been moved. The pressure in pipe I 01 will also be directed to the chamber IIS of of chamber I22 which is for a purpose presently to be described; When only the discharge of the small pump Hill is being directed to the pipe I91, the full discharge from the large supply pump I08 is directed to a chamber I3I of shuttle valve I23 and from chamber I3I the fluid is free to return to the tank I5 by way of pipe I32. If the steering wheel II is turned more rapidlyythe spool valve 16 will move until the spring loaded As the notches Ifia are plunger II2 of pilot valve I3 will ride off the ramp I28. Fluid pressure in chamber H6 from pipe [I4 will now be free to flow to chamber I2I and thence through line, I24 to chamber I22 of the shuttle valve. At this time thepressure from pump I09 is effective in both chambers I22and I29 of the shuttle valve. As the pressure in chamber I22 acts against a larger area of the valve than thepressure in chamber 1 29, the valve will-move downwardly toshut oh the discharge from large pump I08 to supply tank "I5. As a result, the discharge from pump I33 will flow through the'check valve I23 and the combined discharge of both pumps will be directed to pipe ID? to accelerate steering.

When the tractor has, been turned the desired amount relative to the scraper and the steering wheel "II is-no longer in motion, the spool valve will be automatically returned to the neutral position as is shown in Fig. 8 by the follow-up linkage previously described; At this time, the

spring loaded plunger II2 of pilot valve I3 will again rest on the crown of ramp I26 and any the tractor in the manner The valve spool is provided with a plurality of fluid in chamber I I8 will be returned toward the tank by way of pipe II I and return line II9. Furthermore, spring loaded plunger II2 is provided with an: axial bored passage H20; and

spaced radially disposed orts mtserving to vent fluid which leaks past thelands particularly when the plunger is reciprooated in its bore. The vent passages in the plunger II2 serve also to direct the return to supply tank I5 of fluid in chamber I22 which is displaced when the shuttle valve I23 is returned to the position shown in Fig. 8. The return is through line I24,

vent passages in plunger II 2, low pressure chamber H8 and pipe Ill.

The spool valve I6 is shown in Fig. 8 ma neutral position andas having a spring I33 which placed in service to efiect turning. In order to prevent this loss offluid and to maintain the spool I6 which close the ports leading from the lines 4i and 42 when the valve is in its neutral position are provided with notches shown at 16a in their opposite edges which serve to communi cate fluid under pressure entering, through the line Iill' to the lines 4| and 42 and to the jacks.

lands, they serve at once to communicate pressure to the jacks and to relieve excess fluid from the jacks. Due to the restricted orifices created by the notches, a substantial positive pressure is always maintained in the jacks though the bulk of the by-passed through the notches and returns by vay of the line H9 to the tank I5.

With the above described hydraulic circuit, it is possible to efiect slow steering movement by turnin the steering wheel slowly, but if the steering wheel isturned rapidly, the supply of fluid to the lines 4| and 42 is increased to accelerate the steeringmovement.

Fig. 9 illustrates a modifiedform'of control the sliding reception of a valve spool I44 pivot.- ally connected at one end to the link trated in Fig. 5. Slidingof the valve spool in the bore effects distribution of the fluid to the jacks through conduits II and 42 to efiect steerin of previously described.

raised lands IBI, I58, I46 and I47 operate with recesses I52, I54, 42, I 55 formed in the bore of the valve body to effect the desired direction of the fluid therethrough. A spring I45 is associated with one end of the valve spool normally to urge the valve to the central or neutral position illustrated. Fluid from the reservoir MI is admitted to the pumps I42 and I43 by meansof a common supply line as illustrated and isfldirected from thepump I42 to the recess I52 in the valve bore by way of a communicating line I49, while fluid from the pump I43 is directed to the recess I 53 by way of a communicating line I5I.

which co- I53, 4|, and

- With the valve spool in the neutral position Jacks fully primed at all times, thelands of the provided on both sides'of outputfrom the pump is The con- .trol valve is provided with an elongated bore for supply tank 'pump I42 recess I52 in by way crairetum? line I56.

were supply tan free to flowT into the recess I54 and is returned to the tank MI by way of a return line I56.

In. operation, the speed at which the Steering wheel is turned determines the amount of axial movement of the valve spool I44 in the same manner as previously described. When the valve spool is moved to the right, as viewed in Fig. 9, to efiect slow turning ofthe vehicle, the lands m nced recess I 4 and is returned to the ,7

I46 and I4]. enter the bores adiacent to recesses I53 and I55-respectively, so that all of the fluid entering recess I53 from the pump M3 is directed through the power line II to the jacks.

At this time, fluid entering recess I52 from the is still free -to flow into recess I 54 and is returned to tank MI More rapid, turning of the steering wheel moves the spool valve farther to the right-to a position nection.

by way of line I55.

where the land I6! enters the bore between recesses I52 and I54 preventing the fluid in the recess I52 from returning to the'supply tank The resulting pressure rise opens. a spring pressed unloading valve I59 permittingfluid from recess I52 to flow intorecess I53 and thence through the power line Al. Under this condition, all of the fluid from the pumps will be directed to the jacks through power line M to effect faster steering in response to the increased turning speed of the steering wheel.

In a similar manner, rotation of the steering wheel in the opposite direction effects movement of the spool val e I44 to the left preventing fluid in the recess I53 from entering recess 4| thus directing the entire output of the pum I43 to recess 42 and thence throu h conduit 42. More rapid steering is accomplished'bv further mo ement of the valve spool tothe left until land I58 enters the bore between recesses I52 and I54 preventin communication therebetween. At .this

time, the unloading valve 59 opens permitting the entire output ofboth pumps tobedirected 2123A steeringmechanism operable to impart turn movement-1 about :thepivotal draft cone nec xbetween a tractor anda draw implement which comprises.a: lever: pivoted. co.axial y:v with the draft connection and extending outwardly from opposite sides thereof, a pair of fluid actuated jacks pivoted at one end to opposite sides of the tractor andlattheiropposite ends to oppcsite-v ends. of the lever,, a. second pair .of .J'acks pivoted at one end to" opposite ,sides cflthel im'! plement and at their opposite'ifdstothe ends of thelevenmeans to extend one jack in each pair on one side of the tractor and implement and simultaneously retract the other jacks'and gear means to control the swinging movement of thelever relative to the angulardisplacement of the tractor and implement about the draft con- 3. A steering mechanism operable to impart turning movement about the pivotal draft connection between a tractor and a. drawn implement which comprisesa lever pivoted coaxially with the draft connection, power actuated extensible means interposed between the lever and one side of the tractor, and similar means between the lever and the same side of the implement, said means being operable in opposition to each other to impose turning. movement about the draft connection. g a

4. A steering mechanism operable to impart turning movement about the pivotal draft connection between a tractor and a drawn implement which comprises, a lever supported for pivotal movement at a point adjacent the draft connection to extend in a generally horizontal position, a fluid actuated jack between an end of the lever and one side of the tractor, a fluid actuated jack between the same end of the lever and the same side of the implement, andmeans to effect extension and retraction of the jacks in opposition toeach other.

5. A steering mechanism operable to impart turning movement about the pivotal draft con nection between a tractor and a drawn implethrou h the power line lZbv-wav of recesses I53 and 42. The maximum pressure within the svs-- tem is limited bv a pressure relief valve illustrated at I which when open ermits fluid in' recess I53 to flow into recessll and-return to 'supplv tank IM throu h line I51- l'n his m difie form. by inc rporating the urileading valve. in the control valve body, considerable exterior pipin has, been eliminated resultin in a ouicker acting control val e due to the 'jacks pivoted at one end to opposite sides of the implement and at their opposite ends to the ends of the lever, and'means to extend the one jack in each pair on one side of the tractor and implement and simultaneously retract the other Jacks.

ment which comprises, a lever pivoted co-axially with the draft connection, a fluidactuated jack between an end of the lever and one side of the tractor, afluid actuated jack between-the same end of the lever and the same side of the implement, and means to effect simultaneous extension and simultaneous retraction of the jacks.

-6. 'A steering mechanism operable to impart turning movement about the pivotal draft connection between a tractor and a drawn implement which comprises, a lever pivoted substantially co-axially with the draft connection, a fluid actuate'd jack between an end of the lever and one side of the tractor, a fluid actuated jack between the same'end of the lever and the sameside of the implement, means to effect simultaneous extension and simultaneous retraction of the jacks, and gear means associated with .the lever to control the angular displacement of the lever with relation to the angle of turning between the tractor and implement. 1

7. A steering mechanism operable to impart turning movement about the pivotal draftconnection between a tractor and a drawn implement which comprises, a lever pivoted substantially co-axially with the draft connection, a fluid actuatedjack between an end of the lever and one side of the tractor, a fluid actuated jack between the same end of the lever and the same side of the implement, means to effect simultaneous extension and simultaneous retraction of the 11 12 jacks, and gear means between the lever and the e v tractor to compel the lever to swing through one-' V UNITED STATES PATENTS half the turning angle between the tractor and Number Name g D t implement to insure synchronous action of the 130 27 Harrison 1 sepf 13 1933 tWO J 5 2,862,262 French Nov. 7, 1944 CARL A QN- 2,368,202 Clark Jan. 30, 1945 REFERENCES CITED v Choate et a1 Sept. 3, 1946 The following references are of record in the Hukill e Oct. 14, 1947 file of this patent: 1,0 I 

